Platelet-Activating Factor Quantification Using Reversed Phase Liquid Chromatography and Selected Reaction Monitoring in Negative Ion Mode

Platelet-activating factor (PAF) is a potent biologically active phospholipid that mediates human physiological and pathophysiologic responses. PAF levels increase transiently and are typically assessed by techniques with limitations related to expense, sensitivity, pre-analysis derivatization and interference with isobaric molecules. This study elucidates a facile, accurate liquid chromatography–mass spectrometry analytical method for PAF. In negative ion mode using electrospray ionization, collisionally-activated dissociation analysis showed a unique product ion for acetate adducts of PAF molecular species representing the loss of methyl acetate from the polar head group and loss of a part of the acetate group from the sn-2 position. This product ion was exploited for selected reaction monitoring of PAF molecular species following separation by reversed-phase liquid chromatography. Standard calibration responses were determined, and this method was able to detect as low as 100 fmol of PAF. Finally, PAF molecular species were quantified in human neutrophils and monocytes.